The Laser Interferometer Gravitational Wave Observatory
LIGO at the threshold of science operations
Albert Lazzarini
LIGO Laboratory
22nd Meeting of the Indian Association for General Relativity and Gravitation (IAGRG)
11-14 December 2002
Pune, India
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Acknowledgements: LIGO Laboratory
Hanford, WA
Livingston, LA
Caltech
MIT
…just a few of the
many individuals that
have contributed to
LIGO
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LIGO Scientific Collaboration
LIGO I Development Group: 22 Institutions, 26 Groups, 281 Members
http://www.ligo.caltech.edu/LIGO_web/lsc/lsc.html
US Universities:
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Caltech
Carleton College
Cornell University
California State University Dominguez Hills
University of Florida
Hobart & William Smith College
Louisiana State University
Louisiana Techinical University
University of Michigan
MIT
Oregon
Pennsylvania State University
Southern University
Syracuse University
University of Texas-Brownsville
University of Wisconsin-Milwaukee
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US Agencies & Institutions
• FNAL (DOE)
• Goddard-GGWAG (NASA)
• Harvard-Smithsonian
International Members:
• ACIGA (Australia)
• GEO 600 (UK/Germany)
• IUCAA (Pune, India)
International partners (have MOUs
with LIGO Laboratory):
• TAMA (Japan)
• Virgo (France/Italy)
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The LIGO Laboratory Sites
Interferometers are aligned along the great circle connecting the sites
Hanford, WA
MIT
Caltech
Livingston, LA
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LIGO Observatories
GEODETIC DATA (WGS84)
h: -6.574 m
X arm: S72.2836°W
f: N30°33’46.419531”
Y arm: S17.7164°E
l: W90°46’27.265294”
•
Livingston Observatory
Louisiana
One interferometer (4km)
Hanford Observatory
Washington
Two interferometers
(4 km and 2 km arms)
GEODETIC DATA (WGS84)
h: 142.555 m
X arm: N35.9993°W
f: N46°27’18.527841”
Y arm: S54.0007°W
LIGO Laboratory
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l: W119°24’27.565681”
Hanford, WA ->
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Interferometric GW Detectors
Principle of Detection:
•
A gravitational wave causes the
interferometers arm lengths to
vary by stretching one arm while
compressing the other, in the
plane perpendicular to direction
of travel.
Time
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LIGO First Generation Detector
Limiting noise floor
 Interferometry is limited
by three fundamental
noise sources
 seismic noise at the
lowest frequencies
 thermal noise (Brownian
motion of mirror materials,
suspensions) at
intermediate frequencies
 shot noise at high
frequencies
Many other noise
sources lie beneath and
must be controlled as the
instrument is improved
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The Early Years:
Caltech 40 Meter Interferometer
•1/100th scale prototype for LIGO.
•Characterized fundamental noise sources.
•Critical as a technology proving ground.
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Interferometric GW Detectors
Vacuum better than 10-6 torr
1.22 m aperture x 4000 m arms
~9.4 x 103 m3 (each site)
~109 Joule of stored energy
10 kg test masses
<1 nm rms surface error @ l =1.024 mm
Q ~ 106
R>0.99999 @ l =1.024 mm
5m
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Seismic isolation of
ground motion by > 10-6
10 W @ l =1.024 mm
~1020 g /s to split fringe to 10-10
dn/n~10-10
New Window on Universe
GRAVITATIONAL WAVES WILL GIVE A
NEW AND UNIQUE VIEW OF THE
DYNAMICS OF THE UNIVERSE.
EXPECTED SOURCES: BLACK HOLES,
SUPERNOVAE, PULSARS AND
COMPACT BINARY SYSTEMS.
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POSSIBILITY FOR THE UNEXPECTED
LIGO Laboratory IS VERY REAL!
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Timeline to Science
10-17
LLO (LHO) strain noise at 150 Hz
1999
1Q
2Q
10-19 10-2010-21
2001
2000
4Q
10-18
3Q
Inauguration E1
4Q
E2
One Arm
1Q
2Q
E3 E4
2002
3Q
E5
1Q
4Q
E6 E7
Now
3Q
2Q
E8
Power Recycled Michelson
Recombined Interferometer
Full Interferometer
Washington 2K
Louisiana 4k
Washington 4K
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First Lock
Washington
Earthquake
LIGO Laboratory
LHO 2k wire
accident
First
Science
Data
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Sensitivity has steadily improved
throughout commissioning
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LIGO Sensitivity at Start of S1
LIGO
S1 Run
----------“First
Upper Limit
Run”
Aug – Sept 02
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In-Lock Data Summary from S1
Red lines: integrated up time
H1: 235 hrs
H2: 298 hrs
Green bands (w/ black borders): epochs of lock
L1: 170 hrs
3X: 95.7 hrs
•August 23 – September 9, 2002: 408 hrs (17 days).
•H1 (4km): duty cycle 57.6% ; Total Locked time: 235 hrs
•H2 (2km): duty cycle 73.1% ; Total Locked time: 298 hrs
•L1 (4km): duty cycle 41.7% ; Total Locked time: 170 hrs
•Double coincidences:
•L1 && H1 : duty cycle 28.4%; Total coincident time: 116 hrs
•L1 && H2 : duty cycle 32.1%; Total coincident time: 131 hrs
•H1 && H2 : duty cycle 46.1%; Total coincident time: 188 hrs
•Triple Coincidence: L1, H1, and H2 : duty cycle 23.4% ;
•Total coincident time: 95.7 hrs
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LIGO First Science Run Synopsis
• LIGO is now more sensitive than any prior broadband
instrument
• Analysis is in progress
» First pass analysis used ~2.5% of full data set to optimize thresholds, refine
algorithms, techniques
» Collaboration is now analyzing full S1 data set
Not yet ready to quote astrophysical results
Results are being reviewed internally by the collaboration
– Pre-prints should be available by February 2003
– First papers to be submitted by the end of March 2003
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Organization of data analysis working groups
according to source characteristics
• Signals with parametrizable waveforms
» Deterministic
Periodic : http://www.lsc-group.phys.uwm.edu/pulgroup/
Inspiral: http://www.lsc-group.phys.uwm.edu/iulgroup/
» Statistical
Stochastic background:
http://feynman.utb.edu/~joe/research/stochastic/upperlimits/
• Unmodeled sources
» Bursts and transients:
http://www.ligo.caltech.edu/~ajw/bursts/bursts.html
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Time-Frequency Characteristics of GW Sources
Frequency
Stochastic GW
broadband background
Compact Binary BH Ringdown
Inspiral
(After Inspiral)
(Chirp,SNR~30)
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time
frequency
Burst
(Sine-Gaussian)
Burst
(Broadband)
df
 2.6  10 4
f
frequency
Time
Continuous Wave
Source (GW “Pulsar”)
Modulation due
to Earth motion
LIGO Laboratory w.r.t. barycenter
df
 4 10 6
f
time
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LIGO Data Analysis
• Different source searches -> different
analysis methods
• Searches for (short) transient signals
Non-hierarchical Search
» Inspiral: optimal filtering.
» Bursts: time-frequency methods.
•
Searches for (long) periodic signals
» Fourier transforms over Doppler shifted time
intervals.
• Search for stochastic GW background
» Optimally weighted cross-correlated data from
different detectors.
• Detector characterization
» Provide understanding of instrumental couplings
to GW channel.
» Provide calibration for data analysis
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LIGO’s computational needs
dominated by binary inspiral
…
100 GFLOPS @ 1 Solar Mass
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Burst Sources
gravitational waves
Rate
1/50 yr - our galaxy
3/yr - Virgo cluster
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Time frequency characterization of signals
- Exploiting a broadband detector -
merger
chirp
ZM SN bursts
Bandwidth vs. duration
ringdown
ZM SN burst
Generic statements about the sensitivity of searches to poorly-modeled sources
can be made from the t-f “morphology”…
• longish-duration, small bandwidth (ringdowns, Sine-Gaussians)
• longish-duration, large bandwidth (chirps, Gaussians)
• short duration, large bandwidth (merger)
• In-between (Zwerger-Muller or Dimmelmeier SN waveforms)
•These SN waveforms are distance-calibrated; all others are parameterized
by a peak or rms strain amplitude
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Astrophysical Search Pipeline
- example: burst group analysis -
L
L
O
Strain
Data
Quality
Check
Data split
Aux Data
(non GW)
Burst Analysis
Algorithms (DSO)
Feature Extraction
LDAS, DB (T, dT, SNR)
Glitch Analysis
Algorithms (DMT)
Feature Extraction
DB (T, dT, SNR)
…
Aux Data
(non GW)
GW/Veto
anticoincidence
Event Analysis
Tools
Sanity Checks
Simulated data
Based on Astrophysical
Source Knowledge
L
H
O
Strain
Data
Aux Data
(non GW)
…
Aux Data
(non GW)
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Quantify
Upper Limit
Quality
Check
Data split
Burst Analysis
Algorithms (DSO)
Feature Extraction
LDAS, DB (T, dT, SNR)
Glitch Analysis
Algorithms (DMT)
Feature Extraction
DB (T, dT, SNR)
Quantify
efficiency
IFO-IFO
Coincidence
And
Clustering
GW/Veto
anticoincidence
Event Analysis
Tools
Compact Binary Sources
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V. Kalogera (population synthesis)
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Inspiral search
• Dual approach - uses a pipeline process similar to burst search
» Conventional optimal Wiener filtering with chirp templates
– Flat search
• Implemented for analysis of 1994 40m data, TAMA data
» Fast Chirp Transform (FCT)
– Starting with stationary phase approximation to phase evolution, linearize phase
behavior locally to recast filter as multi-dimensional FFT
– Generalize FT:
 FT (t)   df h[ f ] e2 ift 
  CT (t)   df h[ f ] eif ( f )
– Express phase as series in f:
f ( f )  2f  df ( f );df ( f )   k m [ f m ]m
m1
– Discretize to FFT, FCT:
N0 1
 FFT (k )   h[ j] e
j 0
jk
2 i ( )
N0
N0 1
p
 jk
 j  
2 i    lp   

N0 p 1 N0  


  FCT (k,{lp})   h[ j] e
j0
• Hierarchical search - under development
» IUCAA group is a key contributor to this effort
• Multiple interferometer coincidences at the event level
» Coherent processing of strain vector from multiple interferometers still to be
implemented
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Stochastic Background Sources
?
?
Analog from electromagnetic
spectrum
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Stochastic Gravitational Wave
Background
• Detect by
• Good sensitivity requires
>
»(GW wavelength) ~
2x (detector baseline)
»f <
~ 40 Hz
h[f], 1/Sqrt[Hz]
»cross correlating output of
Hanford + Livingston 4km IFOs
LIGO I
Adv. LIGO
• Initial LIGO sensitivity:
>10-5
»W ~
• Advanced LIGO sensitivity:
> 5x10-9
»W ~
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Stochastic Upper Limit Group Activities
•
Analytic calculation of expected upper limits (~100 hrs):

Wfor LHO 2k-LHO 4k will provide the most stringent direct observational upper
limit to date
•
Coherence measurements of GW channels show little coherence
for LLO-LHO 2k correlations
•
Investigation of effect of line removal for LHO 2km-LHO 4km
correlations (e.g., reduction in instrumental correlated noise)
•
Injection of simulated stochastic signals into the data and extraction
from the noise to validate end-to-end capability of analysis
•
Correlations between LLO with ALLEGRO bar detector
»
ALLEGRO was rotated into 3 different positions during earlier E7 run
»
Analysis in progress
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Coherence plots (LLO 4km - LHO 2km)
of strain channel for a few minutes of data
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Measurements of
the Stochastic Background
E7
S1(?)
Goal
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Periodic Sources
Target signals: slowly varying instantaneous frequency, e.g. rapidly rotating
neutron stars in different moments of their evolution.
hc: the amplitude of the weakest signal detectable with 99%
confidence with 4 months of integration, if the phase evolution
were known.

8.5 kpc  f 0 
zz
h  2.3  10  25
c
R  500 Hz 
10 5 10 45 g cm 2


2
I
Data must be corrected for each source position on the sky
* Graphs from Brady, Creighton, Cutler, and Schutz, gr-qc/9702050
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Periodic source searches
Upper Limit Group
3 source categories and 4 algorithms
» All sky unbiased
– Sum short power spectra (no doppler correction)
» Known pulsar
– Heterodyne narrow BW
– Coherent frequency domain
» Wide area search
– Hierarchical Hough transform
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THE CHALLENGE
Generally the phase evolution of the source is not known and one
must perform searches over some parameter space volume
•
The number of templates grows dramatically with the coherent
integration time baseline and the computational requirements become
prohibitive:
1 kHz source,
spindown = 40 yr
0.2 kHz source,
spindown = 1000 yr
On a 1TFLOPS computer it would take more than 104 yr to perform an all-sky
search for f < 1000 Hz for an observation time of 4 months.
* Graphs from Brady, Creighton, Cutler, and Schutz, gr-qc/9702050
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LIGO First Science Run Synopsis
•
•
Quick-look based on ~2.5% sampling of data over 17 days plus Monte
Carlo simulations injected into data subset is complete -- results under
internal review
Compact object inspiraling waveforms
»
»
•
Coverage will include the Milky Way, plus LMC, SMC
Typical sensitivity for a binary neutron star population.
Bursts/transient events
»
»
96 hours of 3X coincidence
2 different (complementary) filters applied to data
– frequency-time clustering algorithm (“tfclusters”)
– time-domain slope detector (“slope”)
– Calibration/efficiency using astrophysically motivated SNe waveforms, wavelets, etc.
•
Continuous wave sources
»
Initial searches target known EM sources, e.g.:
- PSR J1939+2134 (P= 1.557 ms, search and analysis in progress)
– Sco X-1 (in progress - 500 Hz - 600 Hz, multi-parameter search)
•
Stochastic background
»
Limiting sensitivity for Wwill be better than previous direct GW observational
determinations with resonant bars (narrowband)
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Growing International Network of GW
Interferometers
GEO: 0.6km
LIGO-LHO: 2km, 4km
VIRGO: 3km
TAMA: 0.3km
LIGO-LLO: 4km
AIGO: (?)km
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Event Localization With An
Array of GW Interferometers
SOURCE
SOURCE
SOURCE
SOURCE
GEO
TAMA
VIRGO
LIGO
Hanford
LIGO
Livingston
cosq = dt / (c D12)
Dq ~ 0.5 deg
q
1
2
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LIGO Run Schedule
• Science runs are interspersed with engineering runs and
commissioning to bring interferometer to design sensitivity
Now
Nov
E10,…
Oct
Sep
Aug
Jul
LIGO Laboratory
Jun
E9 S2
May
Apr
Mar
S1
Feb
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Jan 2003
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan 2002
E7
S3
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LIGO Interferometer sensitivities continue to improve!!
Recent LIGO Hanford 4 km sensitivity data
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Targeted Noise Spectrum for S2
angular alignment controllers
digital-analog converters
mirror actuators
shot noise (@ reduced power)
S1
S2
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A Look to the Future: Advanced LIGO
• Inherent facility limits
»
»
»
Gravity gradients (seismic waves)
Residual gas (vacuum)
Provides room to improve
sensitivity, increase bandwidth
• Advanced LIGO
»
»
»
»
R&D underway
Seismic noise 4010 Hz
Thermal noise 1/15th
Shot noise 1/10th
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Advanced LIGO:
Cubic Law for “Window” on the Universe
Improve amplitude
sensitivity by a factor
of 10x…
…number of sources
goes up 1000x!
Virgo cluster
Initial
LIGO
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Conclusion
• LIGO scientific operation started with S1 Aug-Sep 2002
» LIGO has started taking data !!!!
» Collaboration is currently carrying out the data analysis
–
–
–
–
Periodic (CW) sources
Compact binary coalescences
Bursts
Stochastic background
• First results should be announced in Feb-Mar 2003
• Detector performance, commissioning continuing to improve
towards design sensitivity
•
Second run scheduled 14 Feb - 15 Apr 2003
» Sensitivity should be almost 10x better than S1
• Planning for second generation interferometers is ongoing
» Proposal for an Advanced LIGO interferometer is under preparation now
» Will include significant GEO participation with UK/German funds
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